1. Field of the Invention
This invention is directed to systems, devices and methods for converting organic material into fertilizer. More specifically, the invention relates to adding iron sulfate or other metallic salts to organic material prior to producing fertilizer from the organic material.
2. Description of the Background
The disposal of sewage sludge is a significant world-wide problem. Current methods of disposing of sewage sludge include incineration, direct land or ocean application, heating and drying the sludge for sterilization and then applying it to land, depositing it in a landfill, or granulating the sludge with a standard rotary granulator with heating and drying being provided by exogenous heat sources (e.g. by burning purchased fuel). While some of these methods result in a fertilizer, such fertilizers are of relatively low analysis with regard to their plant nutrient value.
Methods of expressing a fertilizer's plant nutrient value involve identifying the fertilizer's NPK value, wherein N relates to the amount of nitrogen, P relates to the amount of phosphorus (expressed as P2O5), and K relates to the amount of potassium (expressed as K2O). Thus, as reported in U.S. Pat. No. 3,050,383, sewage sludge with a 2.5/2.5/0 value contains two and a half percent nitrogen, two and a half percent phosphorous as P2O5, and zero percent potassium as K2O. Except as otherwise indicated by usage, all percentage values herein are weight-based percentages (i.e. w/w).
Fortunately, methods exist for enhancing the nutrient value of relatively low analysis organic waste material. For instance, in the aforementioned Wilson patent (the contents of which are entirely incorporated herein by reference), a method is disclosed for treating dried animal manure and sewage sludge with controlled amounts of an acid, such as sulfuric acid, phosphoric acid (or an equivalent phosphorous compound, the strength of which is expressed as phosphoric acid), or mixtures thereof, and an aqueous ammoniacal solution, such as aqueous ammonia or ammoniacal nitrogen salt-containing solutions and tumbling the resulting reaction mass to form fertilizer granules having an upgraded or enhanced plant nutrient value.
Other methods of enhancing the plant nutrient value of relatively low analysis organic waste material with acids, bases, or mixtures thereof have also been described (e.g. U.S. Pat. No. 4,743,287, U.S. Defensive Publication T955,002, Norton et al. (Feb. 1, 1977), U.S. Pat. Nos. 5,466,273, 5,125,951, 5,118,337, 5,393,317, and 5,422,015.
Tubular reactors are known in the art for producing ammonia salts (e.g. U.S. Pat. Nos. 6,117,406, 2,902,342, 2,755,176, and 2,568,901, the contents of which are hereby incorporated by reference). Exothermic reactions are carried out in the tubular reactors by reacting a base with an acid in the reactor tube. European Patent Publication 770,586A1 also discloses that tubular reactors may be used for the treatment of relatively low analysis organic waste material. This European Patent Publication generally describes a process of treating such organic waste by introducing the organic waste, ammonia, and an acid into a tubular reactor, carrying out an exothermic reaction, separating vapor from sludge, and then further processing the sludge.
A component typically associated with tubular reactors is a preneutralizer. The preneutralizer is typically used in conjunction with tubular reactors to effect partial neutralization of the acid prior to its introduction into the reactor. However, the use of a preneutralizer poses various disadvantages including difficulty in obtaining accurate control of flow rates. Additionally, operating and equipment costs associated with the use of a preneutralizer often represent a significant expense.
A reactor similar to the tubular reactor is the pipe-cross reactor. Pipe-cross reactors similarly allow for an exothermic reaction to take place, but typically involve the introduction of one or two different acid solutions for reaction with a base in a method to thoroughly mix the reagents. This is an important feature of pipe-cross reactors as it eliminates the need for a preneutralizer. At the first stage of the cross pipe reactor, the base and/or scrubber water and organic material solution are premixed. At the second step, pipe-cross reactors are formed with up to two acid inlets configured such that the acid solutions are introduced perpendicular to the pipe cross reactor as substantially opposing streams. The perpendicular entry and opposing streams allow for thorough mixing of the acids within the reactor, thus eliminating the need for extraneous equipment such as a preneutralizer.
Pipe-cross reactors are well-known and have been used in the past to produce granular NPKS fertilizers from liquid chemicals (e.g. Energy Efficient Fertilizer Production with the Pipe-Cross Reactor (U.S. Dept. of Energy, 1982) (a pipe-cross reactor fit into the granulator drum of a conventional ammoniation-granulation system); Achorn et al., “Optimizing Use of Energy in the Production of Granular Ammonium Phosphate Fertilizer” (1982 Technical Conference of ISMA, Pallini Beach, Greece); British Sulfur Corp. Ltd., “TVA modifies its pipe reactor for increased versatility”, Phosphorus & Potassium, No. 90, pp. 25-30 (1977); Achorn et al., “Efficient Use of Energy in Production of Granular and Fluid Ammonium Phosphate Fertilizers” (1982 Fertilization Association of India Seminar, New Dehli, India); Salladay et al. “Commercialization of the TVA Pipe-Cross Reactor in Regional NPKS and DAP Granulation Plants in the United States” (1980 Fertilization Association of India Seminar, New Dehli, India); U.S. Pat. Nos. 4,619,684; 4,377,406; 4,134,750; U.S. Defensive Publication T969,002 (Apr. 4, 1978) to Norton et al.; and Salladay et al., “Status of NPKS Ammoniation-Granulation Plants and TVA Pipe-Cross Reactor” (1980 Fertilizer Industry Round Table, Atlanta, Ga., US)). More recently, pipe-cross reactors have been successfully used to enhance the plant nutrient value of relatively low analysis organic waste material (e.g. U.S. Pat. Nos. 5,984,992 and 6,159,263, the entirety of both of which is incorporated by reference herein).
One potential drawback of exothermically treating relatively low analysis organic waste material with reactors, such as a pipe cross reactor or tubular reactor, is the potential for exhausting noxious odors during the process. The use of cross-pipe reactors for treating such waste has helped to reduce the odors typically associated with the treatment thereof. However, a need exists to provide greater assurance that such potential odors are eliminated, or at least reduced beyond current emission levels.
Additionally, a continued desire exists to improve the efficiency of sludge treatment, both in terms of capital expenditure as well as in operating costs.
There is a need in the art for relatively simple and efficient processes for processing relatively low analysis organic waste material to an enhanced plant nutrient value composition without substantial emission of noxious odors. Preferably, such processes would produce products that were sized and shaped to be spread by commercially available commercial spreaders.